Leica APO-Summicron-M 50mm f/2.0 ASPH
More than 30 years after the launch of Summicron-M 1:2/50 mm, which is still available, the Leica APO Summicron-M 1:2/50 mm ASPH. represents a totally new development. With its compact body - only marginally longer and slightly heavier than the Summicron-M 1:2/50 mm, and with an almost identical diameter, it provides visibly higher image quality.
On the Leica APO Summicron-M 1:2/50 mm ASPH. the exceptional correction enables all aberrations to be reduced to a minimum level that is negligible in digital photography. Its key features include excellent contrast rendition, all the way to the corners of the image, even with a fully open aperture. The use of a "floating element" ensures that this is retained, even for close-up shots.
Vignetting is limited to a maximum - i.e. in the corners of the image - of just 2 stops at full aperture in 35 mm format, or around 1 on the Leica M8 models. Stopping down to 2.8 visibly reduces this light deterioration towards the edge of the image, with practically only the natural vignetting remaining.
Distortion is very low at a maximum of just 0.4 % (pin cushion), which is practically imperceptible. A total of eight lens elements are used to achieve this exceptional performance.
To realize the apochromatic correction (resulting in a common focusing plane for three light wavelengths), three are made of glass types with high anomalous partial color dispersion, while two of the others have a high refractive index. The aspherical surface of the first lens in the rear group helps to reduce spherical aberration and flatten the image field. While the optical construction in front of the aperture is a Gaussian type, the arrangement of the lens elements behind it is similar to that in the Summilux-M 1:1.4/35 mm ASPH. This group comprises a "floating element", which is moved independently of the rest of the construction during focusing.